To gain access to treatment sites in the body, catheters must be flexible enough to conform to and follow natural anatomical pathways as they are advanced. These pathways can be quite tortuous, made of soft and delicate tissues with many twists and turns. In the vasculature, this is especially the case, and even more so in certain areas of the vasculature such as the vessels of the brain and the coronary arteries.
When treating a site in the vasculature, the state-of-the-art practice is to first gain access to the treatment site with a flexible, steerable guidewire. Such a guidewire can be precisely controlled by the physician and steered into place using radiographic guidance. Once the guidewire is in-place, the catheter is advanced over the guidewire. The catheter must be flexible enough to smoothly follow the pathway of guidewire. The catheter can, then, be used to deliver the treatment.
In the case of arterial blockage, the catheter may be a balloon dilatation catheter that is used to open the blockage. The guidewire is, first, passed beyond the lesion, and the catheter is advanced over the guidewire and through the lesion. In the case of complete or nearly complete blockage, the force required to advance the guidewire through the lesion can be difficult for the physician to generate by pushing on the flexible guidewire from the arterial access site. Further, this access site may be far from the treatment site, such as in the case of coronary arterial treatment where access to the coronary arteries is gained though the femoral artery. In such a situation, the physician is trying to advance the flexible guidewire through an obstruction over 100 cm away from where he/she is pushing. The same flexibility that helped gain access to the treatment site now inhibits the advancement of the guidewire. The guidewire bends and buckles under the strain and very little thrust is delivered to the tip of the guidewire.
Current practice advances the balloon catheter up to the treatment site to provide support to the guidewire as it is advanced through the lesion. This is an improvement, but the catheter is also very flexible and provides little if any additional support. Specialty support catheters, which offer more support than balloon catheters, are also used. These provide an improvement over balloon catheters but are also limited by how flexible they must be to reach the treatment site.
The above-mentioned problems are compounded in the case of a total arterial blockage or Chronic Total Occlusion (CTO). Accordingly, most CTOs go untreated. And, there is no catheter-based standard accepted practice for CTO treatment. Currently, treatment of CTOs by catheter interventionalists is performed by attempting to pass a guidewire across the CTO. Once the guidewire is across, a low profile balloon catheter can be advanced over the guidewire to dilate the lesion. Such a procedure is almost always followed by placement of a stent. Specialty guidewires are available to aid the physician in this effort but they, too, are limited in their utility by the constraints of flexibility and compliance. It is noted that attempting to cross CTOs is a tedious practice with current equipment and is met with limited success.
Therefore, it would be beneficial to provide a catheter that can advance up to the treatment site with sufficient flexibility through a tortuous path and that can provide sufficient support to advance through a CTO lesion.